The present invention relates to lightning detection, and more particularly to determining the range between an airborne object and a lightning discharge.
Thunderstorms are dangerous to aircraft because of many factors, including violent turbulence, lightning strikes to the aircraft and hail. Increasing use of modern non-conducting materials on aircraft containing sophisticated electronics and fly-by-wire control systems makes them particularly sensitive to thunderstorm electrical hazards.
At present, there are two methods for locating thunderstorms so that they may be avoided by aircraft. A traditional method for avoiding thunderstorms involves the use of radar. Radar, however, has certain inherent limitations restricting its effectiveness. While with an unobstructed view radar can see heavy rain at ranges of 100 miles or more and lighter rain when closer, radar signals are attenuated by precipitation from closer clouds which mask more distant rain. Moreover, rain per se does not necessarily imply the presence of thunderstorms, nor do all thunderclouds produce heavy rain; sometimes they produce no rain. In addition, many aircraft, military as well as civilian (particularly single engine) have no convenient location for radar antennas. Radar also requires appreciable electrical power which may not be available on smaller general avaiation airplanes. Because of the relatively high expense of radar equipment, radar is not used on 95% of the approximately 200,000 general aviation light aircraft in the United States. Furthermore, the thin wings and possible use of nose compartments for armaments or electronic devices are factors which may prevent the use of radar on some military aircraft.
An alternative to radar for storm avoidance is to use radio frequency (RF) emissions from lightning for determining the occurrence and position of lightning which must be associated with thunderclouds. Approximately 10 years ago, a device known as the Stormscope was developed to present a real time display for pilots so that lightning regions could be avoided. This device uses the well-established crossed-looped sensor technique to determine the azimuth of lightning and estimates range from signal intensity. That is, the Stormscope assumes that all lightning flashes are of equal strength with range determined by the attenuation in the received signal. With this apparatus, strong flashes appear too near and weak flashes appear too far away. Both theoretical and empirical evaluations of the Stormscope indicate approximately a factor of two accuracy.
It is therefore an object of the present invention to provide a lightning ranging system having higher accuracy than the Stormscope and to eliminate the inherent limitations of radar discussed above.
It is yet another object of the invention to provide a lightning ranging system which is inexpensive as compared to radar systems.
Yet another object of the invention is lightning ranging equipment which utilizes existing electronic components.